Characterization of heat- and alkali-resistant feruloyl esterase from Humicola insolens and application in the production of high-strength kraft straws.

The application of feruloyl esterase (FAE) in biobleaching can effectively hydrolyze the feruloyl ester bond between hemicellulose and lignin, thereby partially disrupting the dense structure of the fiber, reducing the use of chemical reagents, and obtaining high-performance pulp fibers. Here, we successfully expressed the thermostable alkaline feruloyl esterase from Humicola insolens (H. insolens) in Pichia pastoris GS115, with an enzyme activity yield of 2.36 ± 0.21 U/mL. The highest activity of FAE for the hydrolysis of ethyl ferulate was observed at pH 7.5 and 70 °C. It retained about 56 % of its maximum activity in the pH range of 11.0. After being incubated at 50-55 °C for 1 h, it retained 70.05 % of its maximum activity. The addition of bio-enzyme pretreatment before chemical bleaching can reduce chemical reagents by 20 %, result in a 10.64 % reduction in kappa value, and increase the delignification rate of the pulp by 6.36 %. In addition, the surface of the enzyme-treated pulp showed rougher broom-like fiber filaments, and the viscosity of the enzyme-pretreated pulp (ECP) before chemical treatment increased by 131.51 % compared to the chemically treated pulp (CP), further indicating that the enzyme-pretreated pulp had higher pulp strength.